A clarified culture medium is treated by an ultrafiltration process to recover a secondary metabolite. The density of the fluid is $1020$ kg$/$m$3,$ the viscosity is $1\mathrm{.}8$ cP and the diffusivity of the metabolite is $5\mathrm{.}6$x$10-11$ m$2/$s$.$ The product is recovered with a fluid velocity of $0\mathrm{.}34$ m $/$s in open membrane tubes of $2\mathrm{.}4$ cm in diameter and $2\mathrm{.}0$ m in length. Estimate the mass transfer coefficient k$.$